The present invention relates to cellular telephone systems and to modeling cellular telephone systems for optimizing utilization of the available overall radio spectrum. More particularly, the present invention relates to using measured network data and geostatistical modeling techniques to manage variations and growth within a cellular system and provide improved frequency plans for cellular networks under different variables.
The service area of a wireless communications system is partitioned into connected service domains known as cells, where radio telephone (cellular) users communicate, via radio links, with the base station serving the cell. The cells can be further partitioned into sectors. The base station is coupled to the public service telephone network (PSTN).
Presently available commercial mobile communication systems typically include a plurality of fixed cells each of which transmits signals to and receives signals from mobile units within their respective service areas. In AMPS or FDMA systems, each base station is assigned a plurality of channels (each 30 KHz wide) within a frequency spectrum over which it can communicate with mobile units. A mobile unit within range of the base station communicates with the base station using these channels. Typically, the channels used by a base station are separated from one another in some manner (typically skipping 1, 7 or 21 intermediate channels) sufficiently that signals on any channel do not interfere with signals on another channel used by that base station. To accomplish this, an operator typically allots to a base station a group of channels each of which is widely separated from the next. So long as a mobile unit is within the area in which the signal from a base station is strong enough and is communicating with only that base station, there is only a slight probability of interference with the communication. The present invention will also operate with GSM and iDEN systems which do not rely on the same frequency divisions multiple access method.
In a common type of mobile system called Time Division Multiple Access (TDMA), which includes IS-54 and IS-136, GSM and iDEN each frequency channel is further time divided into additional channels within each frequency. Each base station sends and receives in bursts during some number of different intervals or time slots. These time intervals within frequency bands then effectively constitute the individual channels. In order to distinguish the channel divisions within a frequency and to distinguish channels of a common frequency between overlapping cells digital codes are used. For example, IS-136 utilizes Digital Verification Color Codes unique to a channel at a cell, are used. GSM uses Base Station identification codes.
In order to allow mobile units to transmit and receive telephone communications as the units travel over a wide geographic area, each cell is normally physically positioned so that its area of coverage is adjacent to and overlaps the areas of coverage of a number of other cells. When a mobile unit moves from an area covered by one base station to an area covered by another base station, communications with the mobile unit are transferred (handed off) from one base station to another in an area where the coverage from the adjoining cells overlaps. Because of this overlapping coverage, the channels allotted to the individual cells are carefully selected so that adjoining cells do not transmit or receive on the same channels. This separation is typically accomplished by assigning a group of widely separated non-interfering channels to some central cell and then assigning other groups of widely separated non-interfering channels to the cells surrounding that central cell using a pattern which does not reuse the same channels for the cells surrounding the central cell. The pattern of channel assignments continues similarly with the other cells adjoining the first group of cells. Often adjacent or overlapping cells will transmit on the same frequency and both will be received by a mobile wireless unit. However, because of the digital codes identifying each channel, the mobile wireless unit can process the appropriate signal and ignore any additional reception.
Geostatistics is a xe2x80x9cspatial statisticsxe2x80x9d tool that can be applied to any practical problem of 1D, 2D, or 3D predictions of a random variable. In addition, it can be applied to 4D predictions of spatio-temporal geostatistics monitoring through time. Geostatistics has been used since the early 1950""s for mining engineering, mainly for determining ore reserves estimations and exploitation scenario simulations. Data collected in mining consists of soil cores and cuttings from a limited number boreholes, as well as samples from outcrops. In the early 1960""s a basic theoretical framework of geostatistics had been built that set new standard techniques in the mining industry. Over the past 30 years, this theoretical framework has been strengthened and successfully applied for other types of problems such as fluid flow modeling and subsurface wave propagation. The new applications allow the development of new solutions and new concepts within the framework of an advanced geostatistical theory. The objective of these new developments aim to combine xe2x80x9cspatial statisticsxe2x80x9d and xe2x80x9cdifferential equationsxe2x80x9d describing the behavior of a physical phenomenon. Today, geostatistics is widely recognized as a tool for accurate spatial estimation. Geostatistics has the correct tools to quantify uncertainty and therefore it is considered as a risk assessment tool for field development managers of related industries. Geostatistics has been applied to numerous industrial problems ranging from classical problems of mining oil and gas engineering to more complex and challenging problems such as pricing in a stock market.
Path loss is the attenuation that occurs as RF signals propagate from a transmitting antenna to a receiving antenna. Path loss data sampling, acquisition, and estimation over a cellular network shows great similarities with standard problems encountered in ore-body or reservoir forecasting. Geostatistics has therefore high potential to be implemented for such purposes. The theory of geostatistics applied to physical phenomenon makes it appropriate to use for combining a propagation model and data measurements for wireless network. This application provides for efficiency in collection and maximum use of collected wireless data that results in precise predictions of missing data in a wireless network. The method quantifies and assesses errors due to any measurement or any estimation process. The method provides downscale information and gives RF engineers a high-resolution model describing the path loss over a given area of interest. The method simulates different scenarios of path loss before a drive or between successive drives that would lead to better strategies of data collection.
Geostatistical analysis techniques offer a way of describing the spatial continuity that is an essential feature of many natural phenomenon and provide adaptations of classical regression techniques to take advantage of this continuity. In geostatistics, the application of highly developed algorithms modified to the parameters of the provision of cellular service, as taught in the present invention, yields significantly enhanced results over other data smoothing techniques. The purpose of spatial continuity analysis is to quantify the variability of path loss measurements with respect to distance and direction. Geographic location is only considered if the data exhibit a trend, a property known as non-stationarity. Quantifying the spatial information involves comparing data values measured at one location with values of the same attribute measured at other locations. For example, two path loss measurements in close proximity are more likely to have similar values than two path loss measurements further apart. By determining the correlation with respect to separation distance, estimates of the unmeasured locations can be made based upon the values at the measured locations.